<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
<script>
    //截取前面5个字符,其余用...代替
    //var text = "这是帖子5，主要内容是";
    
    //将大写字母转换为小写字母
    var str = "HELLO JAVASCRIPT";
    var childstr = str.toLowerCase(0,15);
    console.log(childstr);
</script>
</html>